Directional radio receiver



AM E6, 119%. J. R. STEINHOFF DIRECTIONAL RADIO RECEIVER INVENTOR Tia/m 1 5% in/wff Filed March 19, 1938 ATTORNEYS. 2

Patented Apr. 16, 1940 want are Application March 19, 1938,;Serial No. 196,947

9 Claims. (01. 250-11) The present invention relates in general to'directional radio receivers, and more in particular to apparatus of this character which includes some kind of course or direction indicating instrument and which is, adapted to be used as a radio compass or direction finder. The object of the invention is to produce an improved equipment of this character which is highly efficient in use and economical to manufacture.

A special object of the invention is to provide a radio compass or direction finding equipment comprising a smallcompact unit which may be used with standard radio receivers such as are in common use on planes for radio communication. 1

A further object of the invention is to provide a radio compass or direction finder in which only a single directional loop is required.

The invention and other objects'and features thereof will be explained hereinafter with reference. to the accompanying drawing, in which Fig. 1 is a diagrammatic circuit drawing showing the equipment employed in the invention, including a complete radio receiving set; and

Fig. 2 is a fragmentary circuit drawing showing one of several difierent pick-up devices that maybe used as alternatives to the single loop shown in Fig. 1.

Referring to Fig. 1, the reference character 2 indicates a loop comprising a coil of wire wound on a circular supporting ring (not shown). The individual coils, which supply necessary inductance, may be perhaps an inch or. so in diameter, while the loop may be a foot or more in diameter. The opposite ends of .the loop are connected to terminals 3 and 4.

The reference character I represents a direction or course indicator which may be similar to known instruments of this character. It should, however, partake of the characteristics of a voltmeter; that is, it should have a substantial amount of resistance. The reference character M indicates a milliammeter which is used as a distance indicator.

The reference character 8 indicates the operating magnet of a switching device which includes the movable contact members I9, 20, 2!, and 22, and the associated fixed contacts. This switching device may be constructed in various ways, but a device similar to the switching devices used in B eliminators for automobile radio sets and known as synchronous vibrators has been found to be very satisfactory. The switching device shown herein may be therefore similar to a standard synchronous vibrator, except lcud speaker could be used if desired.-

th'at'it is modified by the addition or extra confor use here-is a considerable range of substantially straight line plate current (variation in response to a moderate variation of negative bias applied to the grid, and a sharp cutoff. The

preferably intube mentioned has a plate current drain of .15

about 9 milliamperes' at zero grid bias with a plate potential of about 250 volts, and cuts off at about '7 volts negative grid bias.

There is also shown a manual switch'S, a pair of condensers II andl8, and a condenser 23, 20

together with the necessary circuit connections. The function of these parts will be explained in thecourse of the explanation of theoperation. Below the apparatus so far described there is shown a radio receiver, which, as previously I mentioned, may be of known type. The drawing shows a superheterodyne receiver comprising a radio frequency amplifying tube iii, a combined oscillator and modulator tube 52, an intermediate frequency amplifying 'tube" 53,a combined detector, automatic volume control, and

audio frequency amplifying tube 54, and a power amplifying tube 55. The construction and operation of aradio receiver of this kind is well known, and hence it will not be necessary to describe it beyond calling attention to certain details which will be of interest in the operation of the receiver in connection with the directional equipment. I

The usual tuning element of the set is the gang condenser 56, shown in conventional manner. The manual volume control for the audio frequency output is shown at'59. A pair of head phones for audio reception is shown at 58. A-

The intermediate frequency output: from tube 93 is applied in'the usualmanner to a diode rectifier circuit in tube 54, which not only controls the grid of the amplifying section of the tube, but also serves to provide the variable negative potentials which used for automatic volume control. These potentials are applied to a conductor 5'5, to which the control grids of tubes 5t, 52, and 53 are connected. These same potentials, which vary with the strength of the the magnet 8 of the vibrator.

received signal and range between and 6 volts in the usual set, are also applied over a conductor 63 and a resistor 28 to the control grid of tube 9, as will be discussed more in detail later on. The control grid isconnected to ground through a resistor 29, shunted by a condenser 3|.

A source of direct current. is provided, indicated as a battery B, for supplying direct current to the heater circuits of the tubes and to This battery also supplies power to the B eliminator indicated at 6.

not shown in detail.

The connections between the variousitems of equipment may now be explained briefly, to aid in an understanding of the practical application of the invention.

The vibrator B, the tube (Land the associated circuit elements, including resistors l0 and H and condensers ll, l8, and 23, are preferably all compactly mounted in a casing which is indicated by the dot-and-dash line rectangle 1. The various parts within the casing may be wired to sockets mounted on the wall of the casing and adapted to receive plug terminals of cables through which the unit contained in the casing is connected with the other items of equipment. The switch as may be'mounted on the casing along with the above mentioned sockets.

'In installing the apparatus on a plane, the unit enclosed in the casing 1 may be located at any convenient point, preferably adjacent the radio receiver, to which it may be connected by a cable comprising conductors 24, 25, 2B, and 21. The indicator I, the meter M, and the rheostat RI are located on the instrument panel and are connected with the unit in the casing 1 by means of a cable comprisingconductors [3, I4, l5, and it. A two-conductor cable comprising conductors and Sserves to connect the unit with the loop 2. The various cable connections are shown diagrammatically, but such wiring arrangements are well known and do not require detailed illustration. Q

It will be understood that wherever necessary the circuits should be shielded. It is particularly importantin this connection that the entire radio frequency pick-up circuit be shielded all the way from the loop terminals '3 and 4 to the grid of To accomplish" the tube 5! in the radio receiver. this, shielded conductors of known type are used for conductors 5 and 6. In the vibrator unit, the movable contact members l9 and with their associated fixed contacts may be enclosed in a metal box indicated by the dotted rectangle 30, which is conductively connected to the casing l. The conductor M is also a shielded conductor, and the sheath of this conductor may be used if desired to connect the casing I with the casing of the radio receiver. The various ground connections shown will be understood as indicating connections to the casing l or to the radio receiver casing, which latter is of course conductively connected to the metal frame of the plane in. accordance with the usual practice.

practice signals from an intermediate station may be used, but that is immaterial to the present The latter is of known construction and is For this purpose it will be assumed explanation, it being sufiicient to assume that the desired course is directly toward a certain trans mitting station.

To put the equipment in operation, the switch Si is closed, which connects the battery B to the B eliminator lid and to a conductor 6! over which current is supplied to the heater circuits for the tubes and to the magnet 8 of the vibrator. The radio receiver is thusrendered operative and is tuned to the transmitting station by means of the tuning condensers 5E.

, In the unit 1' the vibrator starts operating. When the'battery B is connected to conductor 65 current is supplied over this conductor and conductor to the magnet 8. The magnet accordingly energizes, but breaks its own circuit at contact member 22, from which it will be understood that the magnet is alternately energized and deenergized and maintains a vibratory movement of the contact members Iii-22 between their respective front and back contacts. The rate of vibration is preferably about 69 per sec- Conductcr 25 also suppli s current to the heater circuit of tube 5, which is thus rendered operative. It may he mentioned also that the necessary plus B potential for the plate circuit of'tube 9 is supplied from 88 over the conductor conductor 26, and through the switch S, the meter M, and the resistor H.

It should be stated at this point that the this type exhibits directional characteristics such that a signal is received with the minimum strength when coming in the plane of the loop and toward the grounded side thereof and with the maximum strength when coming from a direction in the plane of the loop and toward the live or ungrounded side of the loop. Thus in the case of the loop shown, if the axis of the loop is pointing north and south, and if terminal 4 is grounded, signals coming from the east will be received at minimum strength, and those coming from the West at maximum. When terminal 3 of the loop is grounded, the directional characteristics are reversed.

Proceeding with the explanationp it will be assumed that the vibrator is in the position in which it is shown in the drawing, in which posi tion terminal 4 of the loop 2 is grounded over conductor 6, contact member 20, and condenser 23.- It will also be assumed that the plane is properly headed on its course, with the axis of the loop in line with the transmitting station. The loop will accordingly pick up a signal of intermediate strength, considered from the standpoint of the directional characteristic of the loop, which will be transmitted to the radio receiver over conductor 5, contact member 19 of the vibrator, and conductors 24 and 64. The radio receivcr has been tuned to the transmitting station, as previously mentioned, and accordingly the received signal will be amplified in the usual manner. Somewhat more in detaiLthe radio frequency signal is amplified at tube 5|, is converted to an intermediate frequency at tube 52, and is further amplified at tube 53. These operations in the radio receiver are well known and need not be discussed in detail.

The output of tube 53 is transmitted to the diode rectifier circuit of tube 54 by the transformer coupling shown and accordingly a certain negative potential is developed on conductors 5? and 63. The former conductor supplies negative bias potentials to the grids of tubes 55, 52, and

53 for automatic volume control. The latter conductor extends by way of conductor 27 to the control grid of tube 9 and the negative potential thus placed on the control grid limits the plate current through the tube to a certain value. The plate of tube 9 will therefore assume a certain potential and condenser E I will be charged to this potential over a circuit including conductor l2 and contact member ill of the vibrator.

The conditions described in the foregoing obtain only for an instant, as the vibrator is in operation. The effect of the reversal of the vibrator contacts will now be considered.

When contact members i 9 and move to their alternate positions, indicated by dotted lines, terminal 3 of the loop is grounded at contact memoer l9, and the terminal l of the loop is connected over conductor 6, contact member Zll, and conductors M and M to the radio receiver. At the same time the conductor l2 coming from the plate of tube 9 is disconnected from condenser ll by contact member 2! and is connected instead to condenser l8.

As the loop 2 is in the same position relative to the transmitting station as before, the incoming signal will be received at the same strength, and the automatic volume control arrangement at tube 5d of the radio receiver willproduce the same negative potential on conductor 63. It follows that the same negative grid potential is placed on the grid of tube 9, this tube passes the same plate current as before, and the same potential is applied to condenser l8 as was applied to condenser H.

As the Vibrator continues in operation, it will be seen that the terminals l and 3 of the loop are alternately grounded through condenser 23 and connected to the radio set over conductors 24 and 6 3. These operations are carried out at contact members is and 2% At the same time, the conductor 62 is alternately connected to condensers ll and Ill at contact member Zifor the purpose of charging these condensers. Con denser I! is thus associated with the loop (through the radio receiver and tube 9) at times when the loop terminal is grounded, while condenser i8 is associated with the loop at times when the terminal 3 is grounded. So long as the plane stays on its course, the loop picks up the signal from the transmittingstation at the same strength regardless of which of its terminals is grounded, and accordingly the condensers l! and i8 receive equal charges.

The indicator I on the instrument panel is connected across the two condensers El and is by means of conductors l3 and Hi. I So long as the condensers are equally charged. no current can flow through the indicator and its needle or pointer will stand at the zero or mid position.

The indicator circuit arrangement employed,

including the condensers H and i8, is extremely effective and reliable, due to the fact that the condensers charge over circuits containing a minimum of resistance and assume the same charge as the plate potential almost instantly. The operation of the circuit is therefore substantially independent of the vibrator adjustment within a wide range. ciated withcontact member 2i may be adjusted somewhat farther apart than those associated with contact members l9 and 25, so that the condenser charging circuits will be established after the loop switching has been accomplished. No particularly accurate adjustment is needed, however. r ,7 It may be assumed now, that the plane goes off its course to the right. Under this assumption the bearing of the transmitting station will be to the left, and the loop will pick up the signal with greater strength when its terminal 43 is grounded than when its terminal 3 isgrounded. The effect of thisdifference in signal strength may now be explained.

When the strong signal is being received ,(terv minal' l grounded) a higher negative potential will be produced on conductor and onthe grid of tube 9 than before, resulting in a decreased plate current in tube 9. cathode to plate resistance may therefore be, regarded as having been increased, which brings about a The fixed contacts assocharge on condenser l'l. V /hen the weak signal is being received (terminal 3 grounded) the negative potential on conductor $3 and on the grid of tube 9 is less than before, the plate of tube 8 assumes a lower potential. (due to greater plate current), and condenser is is charged to a low er potential than formerly was the case.

Under the condition described, therefore, with the plane off course to the right, the condenser H will be charged each time to a higher potential than condenser 18, and a current flow will be established through the indicator I tending to equalize the charges. The indicator is preferably connected so that under the described condition, with condenser ll receiving the higher charges, the needle will be deflected toward the left, indicating that the bearing of the transmitting station is to the left. The condensers are charged so rapidly that a substantially continuous current is supplied to the indicator, maintaining the needle substantially steady in deflected position.

In order to return the plane to its course, the pilot will turn somewhat to the left. "If he turns too far, the plane will pass through the correct position and will go oiT course to the left. Under this condition the loop will picl; up the signal with the greatest strength at times when terminal It is grounded, with the result that condenser iii will be charged to a higher potential than condenser ll. Current therefore flows through the indicator in the proper direction to deflect the needle to the right.

The amount by which the indicator needle is deflected in any case is dependent upon the amount of deviation from the course and upon the distance from the transmitting station. the plane is close to the transmitting station, large deflections will occur, since the apparatus is sensitive enough to give indications on distant stations. A rh-eostat R is therefore provided and may be adjusted on approaching the transmitting station to make the indicator [less sensitive.

The milliammeter IVE, which is connected in the plate circuit of tube 9, is used a distance indicator. The plate current in tube 9 is a measure of the AVG potential, which in turn depends on the signal strength, oron the distance from the station and on its power output. As the power of the transmitting station is known, the

milliammeter reading may in any case be used to estimate the distance to the station. This device is a useful accessory, but is not essential.

If the pilot desires to listen on the transmitting station with the head phones 58, the switch S may be operated to its alternate position. This stops the vibrator by short-circuiting the interrupter contact 22, and opens the plate circuit of tube 9. The vibrator is stopped by ener izing magnet 8 rather than by merely opening its circuit, in order to prevent accidental shifting of the switching contacts which might occur due to movement of the plane. The plate circuit is opened to prevent the large deflection of the indicator which would otherwise take place. With the vibrator out of action, audio reception is secured in the usual manner with the head phones 58. The volume is adjusted as desired by means of the potentiometer 59.

The operations described in the foregoing re quire merely a fixed loop mounted on the plane with its axis parallel to the axis of the plane. However, a rotatable loop may be used if desired, toenable bearings to be taken from transmitting stations to the right or left of the line of flight. Apparatus for rotating a loop by remote control and for indicating the number of degrees of tation is known. If such apparatus is provided, the bearing of a station off the line of flight obtained by tuning the radio set to such station. and then rotating the loop the required amount to bring its axis in line with the station. When the radio set is first tuned in on the side station, the indicator will be largely deflected, but as the loop is rotated to point its axis at the station. the amount of deflection will decrease and will become zero when the adjustment is completed. The number of degrees of rotation is then read as the bearing of the station. By taking bearings on two stations whose location is known, the position of the plane can be determined in the Well known manner.

Referring now to Fig. 2, there is shown an arrangement con'iprising two directional antennae which may be substituted for the loop shown in Fig. 1. The antennae are indicated at i5 and it and may be straight wires extending parallel to the transverse axis of the plane. The remote ends of the antennae '55 and iii are grounded through resistances Ti and M, respectively. The ground connections may be made to the metal frames of the wings. The inner terminal of the antennae are connected by means of shielded conductors as and ill to the contact members and 20 of the vibrator. The ground connection through condenser 23 is opened or omitted. It will be obvious, of course, that a single vibrator contact member could be used, the moving contact member such as l9 being connected to conductor 24 and the associated fixed contacts being connected to conductors 8B and 8|.

The operation of the modified arrangement will be readily understood in view of the explanation of Fig. 1. The antennaeare directional. If the plane is headed due north, for instance, a signal from the west will be received most strongly by antenna 16, While a signal from the cast will be received most strongly by antenna 75. Signals from the north (or south) will be received with equal intensity. The vibrator connects the conductor 24 alternately to antennae l5 and '56 and at the same time connects the plate conductor 1 2 alternately to the condensers H and it, which are accordingly charged in proportion to the strength of the signal as received by the antennae i5 and 16 respectively. The operation is therefore similar to the operation of Fig. 1.

The invention is also adapted to be used in connection with other types of signal pick-up devices. For instance, two conventional loops may be employed in place of the two straight wire antennae shown in Fig. 2.

From the foregoing it will be seen that although my improved directional apparatus utilises the principle of picking up two signals from a distant transmitter and comparing the strength of such signals in order to determine the bearing of the sending station, it is free from the principal objection to former systems of this type which has made them more or less unsatisfactory. In these prior systems the two received signals were amplified in separate channels, or by separate receivers, which made it necessary to balance or equalize the sensitivity of the two amplifying channels in order to secure a reasonably accurate comparison of the signals. The balancin of two amplifying channels is, however, difficult to accomplish and still more difficult to maintain practice. This difficulty is almost entirely eliminated by my invention, in which a single channel. is used for amplifying both signals, are applied alternately to the amplifier. I

The invention has the further advantage that the principal parts thereof are small and inexpensive and may be conveniently assembled as compact unit for use with known apparatus, such a radio receiver, directional picloup means. and an indicating instrument, to form an efrlciont radio compass or direction finder.

Vlhile I have described certain specific embodiments of my invention, it will be understood that this has been done for convenience and to cilitate the explanation and that the invention is not necessarily limited to the arrangements shown and described, but may be modified in various ways within the principles on which its operation depends. It should be understood, in particular, that although a radio receiver having automatic volume control has been shown, the operation of the equipment as a direction finder does not depend on any AVC action in the receiver. The diode rectifier circuit is merely employed as a convenient means for obtaining a variable negative potential which is proportionate to the applied signal voltage, and this negative potential may or may not be used for automatic volume control. Other arrangements for obtaining the desired variable potential could of course be used.

Under these considerations. it will be understood that I do not wish to be limited to the exact form of my invention illustrated and described herein, but desire to include and have protected by Letters Patent all forms and modifications that come within the scope of the appended claims.

I claim:

1. In a directional radio receiver for an airplane, directional pick-up means responsive to the carrier wave of a distant transmitter and operative' to transmit to said receiver two interspersed series of signals, the strength of the signals in the two series, respectively, depending on the bearing of the said station to the right and left of the line of flight of the airplane, a common means in said receiver for amplifying both series of signals. two condensers, an automatic volume control circuit included in said amplifying means and: arranged to charge said condensers, respectively, in accordance with the strength of the carrier wave in paid two series, and an indicator controlled by re charges on said condensers to indicate the hear-- ing of said station.

2. In a radio direction finding system, a loop antenna directionally responsive to the carrier wave from a remotely disposed transmitting station, a radio receiver, reversible connections between the antenna and the receiver, means for periodically and repeatedly reversing the connections to impress upon the receiver two interspersed series of signals derived from a carrier wave, the strength of the signals in the two series, respectively, depending upon the bearing of the transmitting station to the right and left of the axis of the loop, common means in said receiver for amplifying both series of signals, an automatic volume control device connected to said amplifying means for providing unidirectional potentials proportional respectively to the signal strength in said two series, two capacitors, connections for alternately charging said capacitors, respectively, proportionally to the potentials delivered by the automatic volume control device, and an indicator difierentially controlled by the charges received by the said capacitors.

3. The invention set forth in claim 2, additionally characterized in that the connectionreversing means includes a grounded terminal that is shifted from one terminal of the loop to the other terminal thereof in synchronism with the means for alternately charging the capacitors.

4. In direction indicating apparatus for a dirigible vehicle, directional pick-up means for intercepting the carrier wave from a remotely disposed radio transmitter and operative to provide two interspersed series of signals, the amplitude of the signals in the two series, respectively, depending upon the bearing of the transmitter to the right and left of the direction of movement of the vehicle, means for deriving two unidirectional potentials proportional, respectively, to said two series of signals, at least two capacitors, means for causing said capacitors to acquire individually discrete charges proportional respectively to said two unidirectional potentials and an indicator differentially controlled by the said charges to show the bearing of said transmitter to said pick-up means.

5. In a direction finding system, a space current device having an output electrode provided with a ground connection, a control electrode in said device, at least two capacitors, the high sides of the capacitors being connected respectively to the input terminals of an indicating device, a grounded connection extending between the low sides of the capacitors, switching means for alternately connecting the output electrode to the high sides of the capacitors to provide either a charging or a discharging circuit to ground therefor, and means for impressing unidirectional potentials upon the control electrode whereby the said capacitors may be caused to acquire charges directly proportional respectively to said potentials.

6. The invention set forth in claim 5, additionallyv characterized in that directional radio wave intercepting means are provided for controlling the amplitude of the unidirectional potentials.

7. In combination, a receiving antenna having directional characteristics, means for deriving an unidirectional potential proportional to the radio frequency potential appearing across the terminals oi the antenna during reception of a radio carrier wave, reversible connections between the antenna and the potential deriving means, means for rapidly reversing said connections whereby two series of interspersed unidirectional potential pulses are derived from a single incoming carrier wave, the amplitude of the pulses in each series being proportional, respectively, to the bearing of the carrier wave source to the antentials, proportional to potentials applied to the control electrode, appear when the device is energized, at least two capacitors, an indicating device, connections whereby the indicating device is differentially controlled by electric charges acquired by said capacitors, and automatic switching means for simultaneously connecting the resistor and the space current path in the electric discharge device el fectively in shunt to each capacitor in rapid succession to provide charging or discharging means therefor, whereby the said capacitors acquire discrete electric charges, each charge being substantially continuously proportional to the potential of the control electrode at the instants the respective shunt connections are made.

9. In a direction finding system, an antenna having reversible directional characteristics, means for rapidly reversing the said characteristics whereby two interspersed series of signals are delivered at the terminals of the antenna dur ing the interception of a carrier wave thereby, the amplitudes of the signals depending, respectively, upon the bearing of the carrier wave source to the antenna, means for deriving two unidirectional potentials proportional in magnitude, respectively, to said two series of signals, at least two capacitors, means for causing said capacitors to acquire electric charges respectively proportional to said two unidirectional potentials, and an indicator differentially connected to said capacitors and controlled solely by the said charges.

JOHN R. S'IEEINHOFF. 

